Unable to repair his ship, he sent a sub-plasmic signal, which was detected by Socrates, whose brain was advanced enough to detect the signal. Grimmon hooked Socrates' brain to his craft, and Socrates began to repair it. The Fourth Doctor tracked Socrates to Grimmon's craft, and he fixed the ship for Grimmon, allowing him to return to Jezark. (PROSE: The Brain of Socrates)